It might be a natural feature formation, or possibly a sunken, round man-made object. UFO Battles Captured on Video?

这种形状可能是由一种自然特征所形成，或者也可能是一个沉没在海底的圆形人造物体。

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Image structure information, such as edges and texture, is robust to the illumination change and is the main characteristic of man-made object in high resolution remote sensing imagery.

图像结构信息，如图像的边缘、纹理等，是图像特征的一种，结构信息不易受照度变化的影响，同时是高分辨率遥感图像中的人造目标特性的主要表现形式。

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A structure usually refers to any large, man-made object permanently fixed to Earth's surface or in its orbit, as a result of construction.

结构通常指固定于地球表面或绕地球轨道运行的大型人造建筑物体。

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It measures 5, 500 miles and is the only man-made object observable from the moon.

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On November 17, 1998, Voyager 1 became the most distant man-made object from the Sun when it reached a point further away than NASA probe Pioneer 10, which launched in 1972.

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